This invention relates to the field of electronic measurement and more particularly to a measuring circuit utilizing operational amplifiers to convert an analogue signal into a pulse-width modulated signal which can then be transmitted without information loss to a remote unit for measurement. The signal converter has a first integrator whose summing point is connected to the signal input and also connected to the output of a switching element; and which is then connected in series to a threshold value controller whose output signal actuates the switch element, which in turn provides a positive or negative reference voltage to the summing point and the threshold value controller.
A type of signal converter is disclosed in German published patent application No. 2,135,802. Such signal converters are required for the further processing of potential-separated measured values, e.g., measured values of armature current or of rpm set and actual values in drive designs, when there can be no losses in the information content. In that arrangement the signal is converted into a frequency proportional to the measured value and then transmitted without any voltage information change. On the low voltage side, this frequency is again converted into a voltage proportional to the frequency. It has been shown that particularly in cases of high sampling rates the linearity of this known signal converter is inadequate so that an offset equalization is required, at least in order to avoid expensive, rapid-acting, precision amplifiers to realize the integrator.
In is an object of this invention to provide a signal converter of the type specified above possessing adequate linearity utilizing less expensive operation amplifiers.